genetics of living systems Flashcards
What is a mutation and how could it occur?
Change in the sequence of bases in the DNA which can disrupt protein synthesis
Through substitution, deletion or insertion of one or more nucleotides
What is a frame shift?
A mutation which occurs during an insertion or deletion of a nucleotide.
Addition or deletion which change the reading frame of amino acids and change every excessive read codon from the point of the mutation
What type of substitution mutations can occur?
Silent: A substitution that does not alter the amino acid sequence of polypeptide due to the degenerate nature of the genetic code
Missense: Alters a single amino acid in the polypeptide chain
Nonsense: Creates a premature stop codon which stops the translation of mRNA leading to the production of an incomplete polypeptide
What are the two effects of mutations?
Can have damaging mutations that may stop the synthesis of useful proteins or useful mutations that provide a useful characteristic
What is a chromosome mutation?
A chromosome mutation is a mutation which affects the whole chromosome rather than a section of DNA which can be caused by mutagens.
What are the types of ways chromosome mutations can occur?
1) Deletion: A section of a chromosome breaks off and is lost
2) Duplication: A section gets duplicated on the chromosome
3) Translocation: A section of the chromosome will break off and join another non-homologous chromosome
4) Inversion: Section will break off, reverse and rejoin
What are mutagens?
Mutagens are biological, chemical or physical agents which can alter the rate at which mutations can occur
Why is gene regulation required?
Because certain proteins such as hormones are only required by certain cells at certain times to carry out a short lived response.
The entire genome of an organism is present in the nucleus, including genes not required by the cells therefore expression must be controlled by turning on and off certain genes.
This prevents vital resources being wasted,
In what ways are the genes regulated?
Transcriptional: Genes can be turned on or off
Post Transcriptional: mRNA can be modified to regulate translation
Translational: Translation can be stopped or started
Post translational: Modification of proteins after synthesis
What are histones?
DNA are wound around proteins called histones allowing them to be packed into the nucleus
What is the difference between heterochromatin and Euchromatin?
Heterochromatin is when DNA is tightly wound around histones whereas Euchromatin is loosely wound around the histones.
Why can genes not be transcribed when tightly wound around the histone? (Heterochromatin)
RNA polymerase cannot accsess the genes for translation whereas in losely wound DNA can be freely transcribed.
How can chromatin remodelling be used to prevent energy consumption?
Makes it so that during any other phases of cell division besides from interphase, DNA will be wound tightly as heterochromatin to prevent energy consumption as high energy is required in DNA replication.
How can the strength of DNA wounding around a histone be altered?
HINT: chemistry groups
Histones are (+) whereas DNA is (-)
Acetylation will reduce the positive charge on the histones and make DNA coil less tightly
Methylation will make histones more hydrophobic so they bind more tightly and prevent the transcription of genes.
What is an operon?
An Operon is a group of genes that are under the control of the same regulatory mechanism which are expressed at the same time.
What is the lac operon and what is it responsible for?
The lac operon consist of three genes involved in the metabolism of lactose an can be transcribed into a single long mRNA molecule.
How are the enzymes required for lactose metabolism coded for using the lac operon?
When lactose is present, it binds to the repressor protein and causes it to change shape and no longer bind to the operator.
RNA polmyermase can bind to the promotor and the genes are transcribed and enzymes are synthesised
What is a repressor in an operon?
A repressor is consistently produced and binds to the operator to prevent RNA polymerase binding to DNA and starting transcription. This is coded for via a regulatory gene.
What does the cyclic AMP do?
By binding cAMP receptor protein with cAMP, this will increase the rate at which transcription occurs when RNA polymerase binds to the promotor which is required to produce the quantity of enzymes needed to metabolise lactose
How can a pre-RNA molecule be modified before binding to a ribosome?
mRNA can be stabilised by adding a cap which is a modified nucleotide to the 5’ end and a tail which is a long chain of adenine molecules to the 3’ end which delays degradation in the cytoplasm and assists in mRNAs binding to the ribosome.
What is the difference between introns and extrons?
Introns: non-coding DNA
Extrons: coding DNA
What is splicing?
When RNA is cut at a specific point so the introns are removed and the exons are joined together.
How else can RNA be edited other than splicing and placing a cap and tail?
mRNA molecule sequences can be changed by addition, deletion and substitution which can result in the same effect as a point mutation which increases the range of proteins produced.
What are some examples of translational control?
+The more resistant mRNA is made, the longer it will last in the cytoplasm and the greater quantity of protein will be synthesised
+Binding of inhibitory proteins to mRNA can prevent it from binding to ribosomes to stop protein synthesis
+Activation of initiation factors can help mRNA bind to ribosomes
